<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>Title</title>
    <style>
      ul li {
        float: left;
        width: 100px;
        height: 300px;
        border: 1px solid black;
        list-style-type: none;
        margin-left: -1px;
      }
      ul li:hover {
        position: relative;
        border: 1px solid blue;
      }
    </style>
  </head>
  <body>
    <ul>
      <li>1</li>
      <li>2</li>
      <li>3</li>
      <li>4</li>
    </ul>
  </body>
</html>
